1. Technical Field
The present disclosure relates generally to a hybrid DC-to-AC conversion system and a method of operating the same, and more particularly to a hybrid DC-to-AC conversion system and a method of operating the same to supply a load by different-level DC input voltages.
2. Description of Related Art
Reference is made to FIG. 1 which is a circuit diagram of a prior art two-stage inverter. The two-stage inverter includes a DC-to-DC converter 10A and a full-bridge DC-to-AC converter 20A. The full-bridge DC-to-AC converter 20A is composed of four power switches S1,S2,S3,S4 and diodes connected in parallel to the corresponding power switches. The full-bridge DC-to-AC converter 20A is connected in parallel to the DC-to-DC converter 10A and a DC capacitor C1 is connected between the DC-to-DC converter 10A and the full-bridge DC-to-AC converter 20A to provide buffering of the electric energy. The DC-to-DC converter 10A receives a DC voltage Vdc and the DC voltage Vdc is converted into a capacitance voltage Vc1 by the DC-to-DC converter 10A. Afterward, the full-bridge DC-to-AC converter 20A converts the capacitance voltage Vc1 into a sinusoidal AC voltage with adjustable amplitude and frequency. Finally, the sinusoidal AC voltage is filtered by a filter circuit 30A, which is composed of a first filter inductor L1, a second filter inductor L2, and a filter capacitor Co, to produce an output voltage to supply a load 40A. Note that in order to stabilize the AC output voltage of the two-stage inverter, the capacitance voltage Vc1 has to be greater than an absolute value of the maximum output voltage of supplying the load 40A. Accordingly, the DC-to-DC converter 10A is usually the boost structure to meet the required power for supplying the load 40A, thus stabilizing the output voltage.
However, switching losses of the power switches S1,S2,S3,S4 are proportional to the voltage across the corresponding power switches S1,S2,S3,S4. In order to meet the required power for supplying the load 40A under the condition of that the capacitance voltage Vc1 is greater than the absolute value of the maximum output voltage, more switching losses are generated from the power switches S1,S2,S3,S4. In addition, in order to stabilize the output voltage so that the inverter is the two-stage structure including the DC-to-DC converter 10A and the full-bridge DC-to-AC converter 20A, thus significantly reducing the conversion efficiency.
Accordingly, it is desirable to provide a hybrid DC-to-AC conversion system and a method of operating the same to supply a load by different-level DC input voltages to reduce switching losses of power switches, thus increasing conversion efficiency of the hybrid DC-to-AC conversion system.